Fabrication method of semiconductor device

ABSTRACT

The present invention provides a technology capable of shortening a TAT of a microcomputer with a nonvolatile memory built therein and achieving a reduction in cost. Flash ROMs comprising memory cells each substantially identical in structure to each of memory cells of a flash memory are formed in their corresponding chips lying in a wafer. Subsequently, memory information is written into each of the memory cells of the flash ROM in a probe test process. Thereafter, the memory information written into the memory cell thereof is made unreprogrammable to thereby disable rewriting of the post-shipment memory information. Thus, the shortening of a TAT can be achieved as compared with a mask ROM built-in microcomputer, and management and fabrication costs can be reduced.

BACKGROUND OF THE INVENTION

The present invention relates to a technology for manufacturing asemiconductor device, and particularly to a technology effective ifapplied to a method of manufacturing a semiconductor device having anonvolatile memory, which is mounted on a system LSI (Large ScaleIntegrated Circuit) or the like.

As a general-purpose microcomputer equipped with a nonvolatile memorywhich continues to retain memory information even if power is turnedoff, may generally be mentioned an OTP (One Time Programmable) ROM (ReadOnly Memory) built-in microcomputer or a flash memory built-inmicrocomputer intended for a customer-based soft development ordebugging, or a mask ROM built-in microcomputer intended for a costreduction at mass production, or the like. Here, an OTPROM is anonvolatile memory (inclusive of an EPROM (Erasable Programmable ReadOnly Memory)) capable of writing memory contents therein only once by acustomer, a flash memory is a nonvolatile memory (inclusive of EEPROM(Electrically Erasable Programmable Read Only Memory)) capable ofelectrically effecting all of erasure/reprogramming of memoryinformation, and a mask ROM is a program-fixed nonvolatile memory whichwrites memory information therein in a manufacturing process.

Incidentally, a technology for allowing a plurality of types ofsemiconductor elements to be formed on a sheet of semiconductor waferand enhancing production efficiency of various kinds of semiconductorshas been described in, for example, Unexamined Patent Publication Hei7(1995)-283287 of Iwasaki et al.

Further, a simple manufacturing method of a semiconductor device, whichis capable of effecting writing on a read only memory element of thesemiconductor device having a flash memory element and a read onlyelement together during a semiconductor device manufacturing process andcarrying out reading even without writing after its commercialization,has been disclosed in, for example, Unexamined Patent Publication Hei5(1993)-304277 of Yamamoto et al.

SUMMARY OF THE INVENTION

The present inventors have discussed a method of manufacturing amicrocomputer having built therein a mask ROM as a nonvolatile memory.The following is a technology discussed by the present inventors, andits summary is as follows:

FIG. 8 is a process diagram showing one example of a fabrication processof the mask ROM built-in microcomputer discussed by the presentinventors.

A program for the mask ROM is first developed by a customer (Step 100).This customer program is data-transmitted to a manufacturing site (Step101). Next, the transmitted data is converted (Step 102). Further, amask is fabricated based on the data (Step 103), and wiring patterns areformed on a base wafer (Step 104) fabricated in a wafer process (1) inadvance, using the mask in a wafer process (2) (Step 105), whereby aprototype of a mask ROM built-in microcomputer is manufactured.Incidentally, test items, standards, etc. employed in a subsequent probetest and screening are also simultaneously created upon the dataconversion in Step 102.

Next, whether mask ROM built-in microcomputers formed in individualchips on the wafer are non-defective or defective, is determined by aprobe test (Step 106), and thereafter, a prototype is delivered to acustomer (Step 107). The prototype is evaluated by the customer. When itis determined that no problem occurs in the corresponding mask ROM andthe microcomputer with the mask ROM built therein (Step 108), an orderfor the fabrication of the mask ROM built-in microcomputer is formallyforwarded to the manufacturing site (Step 109). Thereafter, wiringpatterns are formed on the base wafer by use of the mask in the waferprocess (2) (Step 110). Whether the mask ROM built-in microcomputersformed in the individual chips on the wafer are non-defective ordefective, is determined by a probe test (Step 111). Afterwards, thenon-defective mask ROM built-in microcomputers are assembled (Step 112)and their screening according to product standards is performed (Step113), and each of the mask ROM built-in microcomputers each havingsatisfied the product standards is packed and shipped (Step 114).

Incidentally, when a problem on the program occurs in the correspondingmask ROM or the microcomputer with the mask ROM built therein upon thecustomer evaluation in Step 108, the program is discussed again by thecustomer and a mask ROM built-in microcomputer is prototyped andevaluated in a manner similar to the above process steps subsequently.

However, the following problems have become evident after the presentinventors have discussed the method of manufacturing the mask ROMbuilt-in microcomputer.

In the case of a mask ROM, a dedicated mask is fabricated based on acustomer program and each wiring pattern is formed using the mask,whereby the customer program is written into its corresponding basechip. Therefore, the mask ROM has a problem in that a mask chargebecomes a burden regardless of the produced number thereof, and a TAT(Turn-and Around Time) of a manufacturing process becomes long.

Since it is difficult to produce mask ROM built-in microcomputers injust proportion according to the-number thereof by order, they arenormally produced in excess of the required number thereof andthereafter the number of their shipments is adjusted according tocustomer's requests. With a progress of an increase in the diameter ofthe wafer, however, the number of ordered mask ROM built-inmicrocomputers per company is supposed to become fewer than the numberof mask ROM built-in microcomputers obtained from one wafer. In thiscase, there is fear that the original cost of each microcomputer productrises due to the unwanted mask ROM built-in microcomputers.

On the other hand, a microcomputer with a flash memory built therein asa nonvolatile memory grows in demand as well. However, a test processtherefor increases in complexity as compared with the mask ROM built-inmicrocomputer, thus resulting in the occurrence of a problem that theTAT becomes long and its manufacturing cost rises. Therefore, achangeover from all of mask ROMs each having a microcomputer builttherein to flash memories is considered to be difficult.

An object of the present invention is to provide a technology capable ofachieving the shortening of a TAT of a microcomputer with a built-innonvolatile memory.

Another object of the present invention is to provide a technologycapable of reducing the cost of a microcomputer with a built-innonvolatile memory.

The above, other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

Summaries of representative ones of the inventions disclosed in thepresent application will be explained in brief as follows:

The present invention comprises the steps of: forming, in each chiplying within a wafer, a semiconductor device having a nonvolatile memorycomprised of memory cells each substantially identical in structure toeach of memory cells of a flash memory; bringing a probe into contactwith each of electrode pads of the semiconductor device to thereby writememory information into the corresponding nonvolatile memory; anddisabling rewriting of the memory information written into thenonvolatile memory, whereby the memory information written into thenonvolatile memories are made different for each wafer or every pluralwafers, or for each chip in the wafer or every plural chips in the waferto thereby form a plurality of types of nonvolatile memories differentin specification from one another.

Further, the present invention comprises the steps of: forming, in eachchip lying within a wafer, a semiconductor device having a nonvolatilememory comprised of memory cells each substantially identical instructure to each of memory cells of a flash memory; converting aprogram developed by a customer into data; writing memory informationinto the corresponding nonvolatile memory in a probe test process andthereafter probe-testing the semiconductor device having the nonvolatilememory; passivating an erase circuit and a write circuit to therebydisable rewriting of the memory information; assembling thesemiconductor devices each having the nonvolatile memory; and screeningthe semiconductor devices each having the nonvolatile memory, wherebythe memory information is directly transferred to a probe test device,based on instructions given by a production management system after theconversion of the program developed by the customer into the data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process diagram showing one example of a fabrication flow ofa microcomputer with a built-in flash ROM, which is illustrative of oneembodiment of the present invention;

FIGS. 2(a) through 2(c) respectively illustrate examples of layouts ofchips in a wafer, each formed with the flash ROM built-in microcomputerillustrative of the one embodiment of the present invention;

FIG. 3 shows one example of product developments of the flash ROMbuilt-in microcomputers each illustrative of the one embodiment of thepresent invention;

FIGS. 4(a) through 4(c) are respectively process diagrams showingfabrication flows of a flash ROM built-in microcomputer, a mask ROMbuilt-in microcomputer, and a flash memory built-in microcomputer;

FIG. 5 shows one example illustrative of the contents of tests executedin probe test processes of a flash ROM built-in microcomputer;

FIG. 6 illustrates one example illustrative of the contents of testsexecuted in probe test processes of a flash memory built-inmicrocomputer;

FIG. 7 is a circuit layout example in a functional block of a flash ROMconstituting the flash ROM built-in microcomputer illustrative of theone embodiment of the present invention; and

FIG. 8 is a process diagram showing one example of a fabrication flow ofa microcomputer with a built-in mask ROM, which has been discussed bythe present inventors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.Incidentally, members each having the same function in all the drawingsfor describing the embodiments are respectively identified by the samereference numerals and their repetitive description will therefore beomitted.

Incidentally, the term of a semiconductor device in the presentapplication is defined inclusive of ones simply formed not only on amonocrystal silicon substrate but also on other substrates such as anSOI (Silicon on Insulator) substrate, a TFT (Thin Film Transistor)liquid crystal substrate except for a case specified as being not so inparticular.

When reference is made to the number of elements or the like (inclusiveof the number of pieces, numerical values, quantity, range, etc.) in thefollowing embodiments, the number thereof is not limited to a specificnumber and may be greater than or less than or equal to the specificnumber unless otherwise specified in particular and definitely limitedto the specific number in principle. It is also needless to say thatcomponents (including factor steps, etc.) employed in the followingembodiments are not always essential unless otherwise specified inparticular and considered to be definitely essential in principle.

Similarly, when reference is made to the shapes, positional relationsand the like of the components or the like in the following embodiments,they include ones substantially analogous or similar to their shapes orthe like unless otherwise specified in particular and considered to bedefinitely so in principle. This is similarly applied even to the abovenumerical values and range.

FIG. 1 is a process diagram showing one example of a fabrication flow ofa microcomputer with a built-in flash ROM, which is illustrative of oneembodiment of the present invention. The flash ROM described herein is anonvolatile memory constituted by memory cells each substantiallyidentical in structure to each of memory cells of a flash memory, whichis formed using a manufacturing process substantially identical to thatfor each memory cell of the flash memory. The flash ROM corresponds to aprogram-fixed nonvolatile memory which enables writing/erasing of memoryinformation at the stage of its development but disables rewriting orreprogramming of memory information written before its shipment afterits shipment.

Thus, the memory cell of the flash ROM has a one-transistor laminatedgate structure, in which one memory cell is basically constituted of onetwo-layer gate MISFET (Metal Oxide Semiconductor Field EffectTransistor). The two-layer gate MISFET is formed by providing a floatinggate on a substrate with a tunnel insulating film interposedtherebetween and stacking a control gate thereon with an interlayer filminterposed therebetween. For instance, information is stored therein byinjection of electrons into the floating gate.

A base wafer formed with flash ROMs inclusive of wiring patterns ismanufactured and prepared in advance in a wafer process by use of thesame fabrication process as the flash memory (Step 100). Next, a programfor the flash ROM is developed by a customer (Step 101). This customerprogram is data-transmitted to a manufacturing site (Step 102) andthereafter the transmitted data is converted (Step 103). Upon the dataconversion, test items, product standards, etc. used for a post-probetest and screening are also simultaneously created or produced.

Next, writing of memory information into the flash ROMs formed inindividual base chips on the base wafer, and a probe test on the flashROM built-in microcomputer are executed (Step 104). In this processstep, the writing of the memory information into each flash ROM based oninstructions given by a production management system is first executedusing a probe card in which probes are disposed in alignment with fullelectrode pads of the flash ROM built-in microcomputer. Thereafter, adecision as to whether the flash ROM built-in microcomputer is either anon-defective unit or a defective unit, is made on the probe test.Incidentally, the converted data may be transferred directly to a probetest device, based on the instructions given by the productionmanagement system.

Next, a prototype is delivered to a customer (Step 105). When thecustomer evaluates the prototype and determines that no problem occursin the corresponding flash ROM and the microcomputer with the flash ROMbuilt therein (Step 106), an order for the fabrication of the flash ROMbuilt-in microcomputer is formally forwarded to the manufacturing site(Step 107).

Next, writing of memory information into the flash ROM formed in each ofthe individual base chips on the base wafer, and a decision as towhether the flash ROM built-in microcomputer is non-defective ordefective, is made by the probe test (Step 108). The memory informationwritten herein cannot be rewritten or reprogrammed after shipment of themicrocomputer. As will be described later, for example, an erase circuitand a write circuit are passivated to thereby disable the rewriting ofthe memory information. Although the threshold value (Vth) of the memorycell of the flash ROM is relatively set high to write the memoryinformation therein, its wiring may excessively be done.

In the flash ROM built-in microcomputer, the flash ROM constituted bythe memory cells each substantially identical in structure to eachmemory cell of the flash memory including the wiring patterns is formedon the base wafer in advance, and the customer program is written intothe flash ROM by use of the probe card in the process of executing theprobe test. Thus, a TAT of the flash ROM built-in microcomputer can beset shorter than a TAT (corresponding to a period from the reception ofa program from a customer to the delivery of a product) of a mask ROMbuilt-in microcomputer wherein wiring patterns are formed on a basewafer by use of a dedicated mask fabricated after the reception of thecustomer program.

Thereafter, non-defective flash ROM built-in microcomputers areassembled (Step 109). Further, their screening is done in view of theproduct standards (Step 110), and the flash ROM built-in microcomputerseach having satisfied the product standards, are packed and shipped(Step 111). Upon the above screening, the test items that could not bemeasured on the probe test, are tested and appearance conditions andreliability tests or the like are further executed.

Incidentally, when a problem about the program occurs in the flash ROMor the microcomputer with the built-in flash ROM upon the customer'sevaluation in Step 106, the program is re-discussed by the customer, andthereafter a flash ROM built-in microcomputer is re-prototyped andevaluated in a manner similar to the above process steps.

FIG. 2 shows examples of layouts of chips in a wafer, each of which isformed with the flash ROM built-in microcomputer illustrative of the oneembodiment of the present invention.

Since predetermined signals can respectively be inputted to a pluralityof probes provided in a used probe card upon a probe test for writingmemory information into each flash ROM, microcomputers with built-inflash ROMs (e.g., product specification A, product specification B andproduct specification C) different in product specification at eachwafer can be formed (see FIG. 2(a)). Further, microcomputers havingincorporated therein flash ROMs (e.g., product specification A, productspecification B and product specification C) different in productspecification every plural regions or every individual chips can beformed even on a sheet of wafer (see FIGS. 2(b) and 2(c)).

Thus, since the flash ROM built-in microcomputers different in productspecification can be respectively provided in just proportion accordingto the number thereof by order, there is no need to fabricate basewafers equivalent to the same number as the number of productdevelopments and adjust the number of shipped products according tocustomer's requests. Thus, since the number of managements for the basewafers and the number of in-process products are reduced and maskmanagement becomes unnecessary, the cost of managing each flash ROMbuilt-in microcomputer can be set lower than the cost of managing eachmask ROM built-in microcomputer.

FIG. 3 shows one example of product developments of the flash ROMbuilt-in microcomputers each illustrating the one embodiment of thepresent invention.

The present embodiment shows, as an example, a case in which flash ROMbuilt-in microcomputers are developed as products with the flash ROMsbeing changed in specification. The present embodiment illustrates firstthrough tenth product specifications as product specifications. Memoryinformation are written into their corresponding flash ROMs in the probetest process (see Steps 104 and 108) so that individual base chips on abase wafer prepared in advance meet their corresponding productspecifications.

On the other hand, respective dedicated masks used in a wafer process(2) (see Steps 105 and 110 in FIG. 8) are first fabricated according tothe first through tenth product specifications in the mask ROM built-inmicrocomputers. The corresponding mask ROM built-in microcomputers basedon the first through tenth product specifications are formed using themasks. Further, since other ROM products, e.g., OTPROMs or flashmemories or the like are required upon testing of the mask ROM built-inmicrocomputers, there is a need to develop other ROM products.

Thus, since there is no need to fabricate the dedicated masks when theROM products are developed as products, the flash ROM built-inmicrocomputers can be reduced in manufacturing cost as compared with themask ROM built-in microcomputers using the dedicated masks. Further,since other ROM products for testing become unnecessary in the case ofthe flash ROMs, only the flash ROMs may be developed as the ROM productsin the case of the flash ROM built-in microcomputers. The number ofman-hours for circuit design is reduced and the period required todevelop the flash ROMs can be shortened as compared with the mask ROMbuilt-in microcomputers.

Table 1 shows a summary of comparisons of principal items of the flashROM built-in microcomputer showing the one embodiment of the presentinvention and the mask ROM built-in microcomputer discussed by thepresent inventors. ROM Flash ROM built-in Mask ROM built-in Itemsmicrocomputer microcomputer TAT 0.5 to 1 weeks 4 to 6 weeks managementcost relatively low relatively high number of product unnecessary sameas number of developments receptions of customer ROMs mask chargeunnecessary about ¥1,500,000 (6″ wafer) number of types of base 1 2 to 3developed products

A TAT, from the reception of a program from a customer to the deliveryof each product via a development period takes about 4 to 6 weeks in thecase of the mask ROM built-in microcomputer. In the flash ROM built-inmicrocomputer to the contrary, a mask manufacturing step (Step 103 inFIG. 8) and a wafer process (2)(Steps 105 and 110 in FIG. 8) necessaryfor the mask ROM built-in microcomputer are deleted and hence the numberof manufacturing process steps can be reduced. Therefore, a developmentperiod and a manufacturing time can be shortened and the above TAT canbe shortened to about ⅕ or less of the TAT of the mask ROM built-inmicrocomputer like about 0.5 to 1 weeks.

Since the flash ROM built-in microcomputers corresponding to the numberthereby by order, which are different in product specifications, can befabricated, there is no need to fabricate many base wafers correspondingto the dedicated masks as in the mask ROM built-in microcomputers, andthe management cost for each flash ROM built-in microcomputer can bereduced.

Although the dedicated masks of the same number as the number of productdevelopments of ROMs required by the customer in the case of the maskROMs are needed upon development of the ROM products, no masks areneeded in the case of the flash ROMs. As a result, such a mask chargethat the mask ROM built-in microcomputer needs about ¥1,500,000 in thecase of, for example, a 6″ wafer, becomes unnecessary for the flash ROMbuilt-in microcomputer, and hence the manufacturing cost can be reduced.Further, since other ROM products are used for testing of the mask ROMs,ROM products of two to three types (OTPROM, flash memory or OTPROM andflash memory in addition to mask ROM) are necessary for the mask ROMbuilt-in microcomputer. However, since only one kind of flash ROM may beused in the flash ROM built-in microcomputer, a development period canbe shortened.

FIG. 4 is a process diagram showing respective fabrication flows of aflash ROM built-in microcomputer, a mask ROM built-in microcomputer, anda flash memory built-in microcomputer.

In the case of the flash ROM built-in microcomputer showing the presentembodiment shown in FIG. 4(a), a memory cell substantially identical instructure to a flash memory provided with wiring patterns is formedusing the same manufacturing process as the flash memory in a waferprocess. Afterwards, memory information is written into the memory cellin a first probe test process and a flash ROM is thereafter tested infirst and second probe test processes, followed by execution of tests onthe functions/performance and the like of a RAM and logic in a thirdprobe test process. Each flash ROM built-in microcomputer judged to benon-detective on the probe test is assembled and its screening accordingto product standards is performed in a final test.

In the case of the mask ROM built-in microcomputer shown in FIG. 4(b), amemory cell unprovided with wiring patterns is formed in a wafer process(1). In a wafer process (2) subsequent to the above, wiring patterns areformed using dedicated masks, and memory information is written into thememory cell. Thereafter, tests on performance/functions and the like ofa mask ROM, a RAM and logic are performed in a probe test process. Eachmask ROM built-in microcomputer judged to be non-defective in the probetest process is assembled in a package process and its screening basedon product standards is performed in a final test.

In the case of the flash memory built-in microcomputer shown in FIG.4(c), a memory cell provided with wiring patterns is formed in a waferprocess. Next, a test on a flash memory, using a dedicated memory testeris performed in first and second probe test processes, followed byexecution of functions/performance and the like of a RAM and logic in athird probe test process. The corresponding flash memory built-inmicrocomputer judged to be non-defective in each of the first, secondand third probe test processes is assembled in a package process, andits screening based on product standards is performed in a finalprocess. In the final process, a test on the flash memory, using adedicated memory tester is first performed in a first final process, andtests on the RAM and logic are carried out in a second final process.

One example descriptive of the contents of tests on a flash ROM in probetest processes (1) and (2) of a flash ROM built-in microcomputer isshown in FIG. 5, and one example descriptive of the contents of tests ona flash memory in probe test processes (1) and (2) of a flash memorybuilt-in microcomputer is shown in FIG. 6.

As the contents of the tests on the flash ROM, may be mentioned, forexample, a write test, a read test, a disturb test, and a read testsubsequent to wafer bake, etc. On the other hand, the contents of thetests on the flash memory may include, for example, a read test, a writetest, an erase test, a disturb test, high-temperature retentionsubsequent to wafer bake, deplete test, etc. Items for the respectivetests also range widely.

Since the flash ROM built-in microcomputer needs not to execute suchwide-ranging tests peculiar to the flash memory, which are performed inthe flash memory built-in microcomputer, the number of test processescan be reduced to about {fraction (1/10)} as compared with the flashmemory built-in microcomputer, and no dedicated memory tester isrequired either. Accordingly, the TAT of the flash ROM built-inmicrocomputer can be set shorter than the TAT of the flash memorybuilt-in microcomputer. Owing to a reduction in capital investment cost,the flash ROM built-in microcomputer can be reduced in product cost ascompared with the flash memory built-in microcomputer.

Incidentally, the test of detecting such a retention failure that memoryinformation written therein disappears, is performed upon the read teston the flash ROM in the flash ROM built-in microcomputer. Since,however, the flash ROM is capable of excessively performing writing, forexample, as compared with the flash memory, the flash ROM built-inmicrocomputer does not necessarily require the retention test.

FIG. 7 is a circuit layout example in a functional block of a flash ROMconstituting the flash ROM built-in microcomputer illustrative of theone embodiment of the present invention. In the drawing, referencenumeral 1 indicates a flash ROM user utilizing area, reference numeral 2indicates a flash RPOM unopen area, reference numeral 3 indicates afirst read circuit, reference numeral 4 indicates a second read circuit,reference numeral 5 indicates a write circuit, and reference numeral 6indicates an erase circuit, respectively.

A customer program is written into the flash ROM user utilizing area 1.Upon shipment of the flash ROM built-in microcomputer, the write circuit5 and the erase circuit 6 are passivated and memory information of theflash ROM cannot be rewritten or reprogrammed after the shipmentthereof.

There is a need to set a threshold value of each of memory cells of aflash memory to within a predetermined range. When the threshold valuefalls out of this range, the flash memory is judged to be defective. Inthe flash ROM, however, a relatively high threshold value and arelatively low threshold value are determined and memory informationwritten into the corresponding memory cell is read. Thus, since thememory cell of the flash ROM can take its threshold standard rangewidely as compared with the flash memory, the production yield of theflash ROM built-in microcomputer becomes higher than that of the flashmemory built-in microcomputer.

Thus, according to the present embodiment, the mask fabrication processand the wafer process (2) for forming the wiring patterns, which arerequired for the writing of the memory information in the mask ROMbuilt-in microcomputer, become unnecessary for the flash ROM built-inmicrocomputer, the TAT of the flash ROM built-in microcomputer can beset shorter than the TAT of the mask ROM built-in microcomputer.

Since the flash ROM built-in microcomputers different in productspecification can be respectively provided in just proportion accordingto the number thereof by order as well, the flash ROM built-inmicrocomputers can be reduced in management cost as compared with themask ROM built-in microcomputers.

Further, when each ROM product is developed, the flash ROM built-inmicrocomputer needs not to fabricate the dedicated mask and can bereduced in manufacturing cost as compared with the mask ROM built-inmicrocomputer. Since the flash ROM built-in microcomputer does notrequire other ROM products for testing, the number of man-hours forcircuit design is reduced and hence its development period can beshortened, as compared with the mask ROM built-in microcomputer whichneeds other ROM products for testing.

Still further, since the flash ROM built-in microcomputer does notrequire wide-ranging tests peculiar to the flash memory, which have beenperformed in the flash memory built-in microcomputer, the TAT of theflash ROM built-in microcomputer can be shortened as compared with thatof the flash memory built-in microcomputer.

Still further, since each memory cell of the flash ROM can take athreshold standard range widely as compared with the flash memory, theproduction yield of the flash ROM built-in microcomputer can be sethigher than that of the flash memory built-in microcomputer.

While the invention developed above by the present inventors has beendescribed specifically based on the illustrated embodiments, the presentinvention is not limited to the embodiments. It is needless to say thatvarious changes can be made thereto within the scope not departing fromthe substance thereof.

While the above embodiment has described, for example, the case in whichthe invention is applied to the ROM product built in the microcomputer,the present invention is not limited to it. The invention can be appliedeven to a ROM product fabricated as single, for example.

While the memory cell of the flash ROM is set to substantially the samestructure as the memory cell of the flash memory in the illustratedembodiment, the memory cell thereof can be set to substantially the samestructure as, for example, a memory cell of a ferroelectric RAM (RandomAccess Memory) in which a ferroelectric film is caused to have a writefunction, or a memory cell of an MRAM (Magnetoresistive Random AccessMemory) using the direction of magnetization of a ferroelectric body inan information memory carrier.

Advantageous effects obtained by a representative one of the inventionsdisclosed in the present application will be described in brief asfollows:

As a nonvolatile memory built in a microcomputer, a flash ROM is adoptedwhich includes memory cells each substantially identical in structure toeach of memory cells of a flash memory and which writes memoryinformation therein in a probe test process and disables rewriting ofthe memory information after its shipment. Thus, the shortening of TATcan be achieved as compared with a mask ROM built-in microcomputer, andmanagement and fabrication costs can be reduced. Further, the shorteningof TAT can be achieved as compared with a flash memory built-inmicrocomputer, and production yields can be enhanced.

1-15. (cancelled)
 16. A method of fabricating a semiconductor device, comprising the steps of: (a) forming a logic circuit and an electrically reprogrammable ROM circuit each having substantially the same structure in each of first and second chip areas on a wafer; (b) discretely or simultaneously executing a first electrical operation test on the first and second chip areas in a state of the water; (c) after said step (b), respectively electrically writing first and second ROM pattern data corresponding to first and second user's uses into the ROM circuits in the first and second chip areas respectively, as a step prior to or below the first electrical operation test; (d) dividing the wafer into the first and second chip areas after said step (c); and (e) executing a second electrical operation test on the divided first and second chip areas respectively.
 17. The method according to claim 16, wherein prior to said step (d), the first and second ROM pattern data are made unerasable or unreprogrammable according to an electrical signal operation normally open to a user.
 18. The method according to claim 16, wherein the first and second ROM pattern data are identical to each other.
 19. The method according to claim 16, wherein the first and second ROM pattern data are different from each other.
 20. The method according to claim 16, wherein the electrically reprogrammable ROM circuit has a structure corresponding to a flash memory circuit.
 21. The method according to claim 16, wherein the electrically reprogrammable ROM circuit has a structure corresponding to a ferroelectric RAM circuit.
 22. The method according to claim 16, wherein the electrically reprogrammable ROM circuit has a structure corresponding to an MRAM circuit.
 23. The method according to claim 16, wherein a retention test is unexecuted on the electrically reprogrammable ROM circuit before at least said step (d).
 24. The method according to claim 16, further including a step of: (f) executing a retention test on the electrically reprogrammable ROM circuit as a step prior to said step (d) and after said step (c) or therebelow. 